Mechanically attached connections such as fittings, joints, couplings, unions and so on are used in fluid systems to contain fluid flow. Such mechanically attached connections may be conduit fittings for tube, pipe or any other type of conduit. The conduit fittings may connect a conduit end to either another conduit end or to another portion of a fluid system. For simplicity and clarity, the term ‘fitting’ as used herein is intended to be all inclusive of other terms, for example coupling, connection, union, joint and so on, that could alternatively be used to refer to a mechanically attached connection. Such mechanically attached connections are characterized by a fluid tight seal and mechanical strength to hold the connection together including sufficient grip of the conduit under vibration, stress and pressure. Fluids may include gas, liquid and any variation or combination thereof.
Fluid systems typically use mechanically attached connections to interconnect conduit ends to each other and to flow devices which may control flow, contain flow, regulate flow, measure one or more characteristics of the fluid or fluid flow, or otherwise influence the fluid within the fluid system. The term ‘mechanically attached connection’ as used herein means any connection for or in a fluid system that involves at least one connection that is held in place by mechanically applied force, stress, pressure, torque, or the like, such as, for example, a threaded connection, a clamped connection, a bolted or screwed together connection and so on. This is distinguished from a metallurgical or chemical connection most commonly practiced as welding, brazing, soldering, adhesive and so forth. A connection may include a combination of mechanical and metallurgical connections, and often do, and such connections are also within the term ‘mechanically attached connections’ as they include at least one such connection.
One example of a mechanically attached connection involves a conduit gripping device, such as, for example, a collet or one or more ferrules, which may be installed on an outer surface of a conduit for assembly with a fitting. In a conventional ferrule type fitting, first and second coupling members (e.g., a fitting body and nut) may be assembled together and tightened (or pulled up) to install the ferrule or ferrules in gripping and sealing engagement with the conduit by plastically deforming the ferrule or ferrules on the conduit. The installed ferrule or ferrules provide a fluid tight seal with the assembled fitting, particularly under pressure, as well as adequate grip of the conduit and protection against vibration fatigue.
Ferrule type fittings are well known and characteristically include a threaded coupling nut, a threaded coupling body and one or more ferrules that fit inside the coupling nut. The coupling body typically includes a camming surface that engages a camming surface on a ferrule. A cylindrical conduit such as, for example, a tube end, is slid into the coupling body with the ferrules closely surrounding the outer wall of the conduit end. When the coupling nut is installed onto the threaded end of the coupling body (or vice versa when the coupling body includes female threads), an axial force is applied to the ferrule or ferrules which causes the camming surfaces of the ferrule and body to engage to produce a swaging action thereby causing a radial displacement of portions of each ferrule, causing the ferrules to tightly grip the outer wall of the conduit end. In many applications the fitting can be assembled with the use of simple hand tools such as wrenches.
In some circumstances, a fitting's conduit gripping device may be “pre-installed” or “pre-swaged” on a conduit (using, for example, the fitting with which the conduit gripping device is to subsequently be assembled, another fitting, or an installation tool) to facilitate subsequent installation of a fitting to the conduit in the fluid system. For example, tools may be used to “pre-install” or “pre-swage” the such one or more ferrules on the conduit, which holds the one or more ferrules and the coupling nut on the conduit as a subassembly. This subassembly of the ferrules, coupling nut, and the conduit are later assembled with a fitting body to form a final fitting assembly. One example of a tool for swaging ferrules onto a conduit is disclosed by U.S. Pat. No. 6,834,524 to Johnston, titled “Apparatus for Swaging Ferrules,” which is incorporated herein by reference in its entirety.
Another example of a mechanically attached connection is known as a flared fitting. In a flared fitting, an end of the tube that seals with a fitting body is flared radially outward. Some existing flared fittings include a body, a sleeve, and a nut. The nut and sleeve are placed over the tube and the tube end is flared radially outward. After the flaring operation, the flared tube end is clamped between the fitting body and the sleeve by the nut.